Salt bath system and method for treating metals



March 13, 1956 H. R. SPENCE 2,738,294

SALT BATH SYSTEM AND METHOD FOR TREATING METALS Filed Sept. 13, 1951 2: I 12 5 8 J7 a J I I I I I l I I l I OI H] &

-r i I 4 JE 3 INVENTOR Harry E 6,00006 SALT BATH SYSTEM AND METHOD FOR TREATING IVIETALS Harry R. Spence, Pittsburgh, Pa., assignor to Diamond Alkali Company, Cleveland, Ohio, a corporation of Delaware Application September 13, 1951, Serial No. 246,371 r 14 Claims. (Cl. 134-42) This invention relates to a new bath system and method for treating metals and an universal alkaline salt composition for use therein in a fused state. More particularly, this new system comprehends electrolytic and non-electrolytic bath operations on ferrous and other metals using a new salt which is preponderantly caustic soda and which contains caustic potash andan alkaline earth metal halide. Still further, this new salt bath system enables such metals under selected conditions of operation to be cleaned, descaled, desanded and/or heat treated.

There are a number of processes which employ sodium hydroxide alone or with other ingredients purportedly to clean or descale ferrous and non-ferrous metals in nonelectrolytic or electrolytic baths. In many cases, the compositions so used whether oxidizing or reducing in nature, relatively quickly becomecontaminated and ren- Figure l is an illustration in side elevation and partial section of one form of salt bath equipment, without .the cover thereon, which may be used to practice my new system under electrolytic conditions;

Figure 2 is a section of the equipment shown in Figure 1 taken along line IIII thereof; and

Figure 3 is a plan view of the equipment shown in Figures 1 and 2.

My new composition consists essentially. of caustic soda (NaOH), caustic potash (KOH) and an alkaline earth metal ha 'de such as barium chloride (BaClz).

. These ingredients of the new composition will gen- NaOH, about 95%;

der it ditficult to produce clean work. Some salt compositions further require particular precautions to avoid undue build-up of an explosion potential or frequently can only be carried out at relatively low temperature or at low'rates of effective activity. In other cases using prior salt compositions, the work treated is stained or left with an adherent coating, generally in the nature of an oxide, which is difiicult to remove by conventional pickling methods. Examples of such prior practices are set forth in United States Patents Nos. Re. 22,887, 2,134,457, 2,261,744, 2,311,099, 2,353,026 and 2,458,660...

In the new system of this invention, the difficulties and objections encountered in the practice of the foregoing prior operations are overcome. Thus, I have produced a new salt composition for use in a fused state at temperatures generally in the range from about 650? F. to about 1350 F. That in my new system under non-electrolytic or electrolytic conditions. In my operation, I find also that I may em-' ploy lower temperatures for cleaning or lighter deoxidiz-' ing and somewhat higher temperatures for descaling or desanding. In the upper portion of the temperature range, annealing or tempering of the work may also be achieved without any attack by the salt upon the base metal of the work in the course of its treatment by my new system. Generally, under electrolytic conditions, as distinguished from non-electrolytic operation, the temperatures employed will be relatively lower for descaling or desanding and I avoid non-uniformity of result or other difliculty by positioning the work between the electrodes without making it one of them. In addition to the prime quality of the work produced by it, my salt bath system, whether a non-electrolytic will resist oxidation and contamination and will retain its activity for greater periods of time for comparable tonnages treated. My new salt composition will also avoid becoming materially changed in the respective proportions of the ingredients in it.

Other objects and advantages will be apparent from the following description and from the drawings, which are schematic only, in which new composition may be employed or an electrolytic operation,

about 98%; KOH, about 1.5%;

. castings.

My new composition may have the following respective proportions on a dry weight basisNaOH, from about 70% to about 95% KOH, from about 0.5% to about 12%; BaClz, from about 0.5% to about 20%.

erally be of a commercial grade of purity which, for example, in the case of sodium hydroxide usually includes from /2% to as much as 3% of sodium chloride by weight. For non-electrolytic applications, my new composition may have a range of the foregoing ingredients in the following proportions on a dry weight basis NaOH, from-about to about KOH, from about 0.5% to about 4.5%; and BaClz, from about 0.5 to about 12%. A particular charge for use as a fused salt may have a composition for non-electrolytic operation of the following proportions on a dry weight basis- KOH about 4.5% and BaClz about 0.5%. Similarly, for electrolytic applications, my new composition may have a range of proportions on a dry weight basis as follows-NaOH, from about 70% to about 98%; KOH, from about 0.5 to about 12%; and BaClz, from about 0.5% to about 20%. A particular charge for electrolytic operations may have a composition in following proportions on a dry weight basis-NaOH,

In the operation of my new system, a temperature range may be availed of between from about 650- F. to about 1350 F., with a sufficient time of treating in each case to produce the result desired on the work. The number and type of work of metals and metal alloys that may be treated, the oxide, scale, sand, or other surface conditions thereof, comprise factors influencing in the treatment of the work by my new system the particular temperature and time relation to be employed. Temperature and time constitute conditions which to some extent may be interchangeable in the course of the employment of my new system as will be well understood by those skilled in the art. In general, cleaning off of grease, paint or lacquer coatings, enamel or dirt, for example, or the removal of lighter oxides from the surface of the work may employ a temperature from about 800 F. toabout 900 F. in anon-electrolytic operation where no simultaneous annealing or tempering is to be sought. For the removal of heavier oxides or scale or fordesanding castings, for example, a temperature range from about 800 F. to about 1050 F. may be utilized in non-' electrolytic applications. Another non-electrolytic operation of my new system under the conditions recited will reclaim rusty iron, steel and other'ferrous metal alloys such as thosefound in machine tools, nuts, bolts, shell cases and gun tubes to produce high quality scrap metal My new system will also remove all carbon in the form of graphite such as is sometimes found on the surface of the work such as cast iron base metal of the work. Temperatures between the melting point of the new composition, in'the neighborhood of 650 F. depending upon the respective proportions of the ingredients therein, and about 800 F. may be employed with a somewhat longer time and BaClz, about 0.5%.

Higher temperatures within the broader range 1 may .also be employed without adversely affecting the which usually will be of treatment being accorded. In general, no temperature nor length. of time ofi treatment will exceed that-required to obtain the desired result on the surface of the work.

The time of the foregoing treatments may vary from a minimum of about 15 seconds to a maximum of about 2 /z hours, during which the work will be immersed in and. subjected tothe action of my new saltwhile ina fused state in a suitable potor container. The temperature of the fused composition in the containerisgenerally maintained as relatively constant as possible by any of: thevarious heating furnaces or other heating means available.

Heat treatment, tempering or annealing of the work maybe accomplished in addition to cleaning, deoxidizing, descaling, and/or des'anding. In the cases' of suchheattreatment utilizing a fused salt. of my new system, the temperature range maybe varied for theefiecr desired fromabout 1000 F. to about 1325" F; with-a maximum temperature of about 1350 F. For example, spheroidizing. may be obtained by my new system on. ferrous plates or. strips right from the hotrolling millsat a temperature in the neighborhood of 1250 F. in a treat mentiperiod of. about one hour. Further, annealingw-ill generally. not; exceed a treatment periodof about one hour: by-my new. system; Similarly, armor plate may begivenadrawback treatment at a temperature of betweenfrom about; 1050? E. toabout 1250 F; for a relatively shortlengthtofitime to develop the desired characteristicsinthesteel without impairing itsother qualities.

The desanding of castings or the descaling of=forgings=- with. attendant heat treatment may be obtained in theapproximate temperature range between from about 1059: Frtoabout 1250 F. for a sufficient time. In general, a. treatment timebetween fromabout 15 seconds toabout 2% hourszwill besufiicient. Forexample, gray ironicastings .for. automobile transmissions may be treatedunder non-electrolytic conditions in my new salt bathsystemnat;a,temperature of about.1200' F. for about 4 /3 minutes: during. which time the metal is completelyanneale'd; stress-relieved, desanded anddescaled. The-cast ings aftenbeingremoved from thebath are air cooled for aboutl" minutes, water. quenched at roomtemperature: andthen given. about a thirty second dip-in 7% warm sulphuric,-,acid. The acid dip maybe followedby a=hot= water rinse=and1that in turn by a water solub'leoi-l dip to preteen the castings .against atmospheric corrosionduring storage. The same castings may be descaled and desanded'ina non-electrolytic operation at a temperature' from-between about 850 F. to about 900 F. If'steam is introduced; into the: new: fused salt bath thesulphuric acid; dip and water soluble oil dip maybe omitted and the-castigrgswillbeeven lighter gray incolor.

In the case;.of;some metals such as stainlesssteelc'om tainingioveri about'11%- chromium, stress relief-cambeobta d bybr-inging:thematerial upto a:stress relieving temp lure; without holding it at that temperature. Such; for; example; isthecase with stainless" steel wirewhich has been coldworked. The stress introduced by the;cold'; working. can be removedin the-fused salt' bath imlc$ifl13f1zl5 seconds; if it takes less time than that for the: wire to;.' reach bathsstress relievingtemperature. The longenperiods oftime such as 2 /2- hours w'ouldbe thoseer-nployed, for example, in. batch asdistinguished" fromcontinuousoperations. In the descaling of hot rolled steel bandstin acontinuous operationby-mea'ns of" my new: system,. about. thirty minutes would generally" be thernaximum time the bands might be maintained in a moving. condition in the bath.

My new composition may also be usedin a fused saltbath operatingiunder electrolytic conditions- By way of illustration-and not limitation, Figures 1' to 3 schematical ly.ill ustrat e; a-,form-of. equipment usable for such pur poges ThuS,.aimetalcontainer or vessel 10' usuallymade of .steel -haying :vertical sides 11 and ends 12 maylbe'fill'ed to;an apprepriatetlevel 13. withafused' salt' of my n'ew composition; Foreignmaterial which-settles imthe bath in the course of the use thereof will fall into the pans 14 placed on the bottom of the pct 10; Thereby, the scale, sand, oxide, rust and/ or other contaminant settling into the pans 14 can be removed periodically by removing the cover (not illustrated) of vessel 10 and lifting out the rolls before removing the pans. 14 by means of crane hook slings engaging the eye-lugs 15 fastened to the edges of. the pans. 114.

Stirring of the fused salt; bath may be obtained through the medium of an impeller 21 driven through shafts.22 and 23, universally coupled together. A motor 24. may be employed to turn shaft 23 and rotate impeller 21. Sinker rolls 25 may be journaled on the respective sides 11 of vesseli 10 to define between them the level at which the work, such as ferrous strip-26, moves through the bath 13. Guide rolls 2'7'and 28 may also be employed and extend between the sides 11 of the vessel 10 where they are suitably journaled. The rolls 28 also, tend to wipe off the surface of work. 26 and reduce, the amount of.dragout of salt from the bath 131 Pinch rollers29 drivenat a predetermined speed provide the motive power fon moving work 26 through the fused salt in vesselll) at a. rate determining the selected time of immersion of work.26.

Steam or' water injection pipesv 39 may bev provided. extending. downwardly inside vessel 10 below level 13 therein. Valves 31: are provided in respect topipes- 30 to regulate the flow of steam or water if any, which. may be passed through the body of fused salt 13. If. water is injected as may be done in a majority of cases,. the valves 31* may be needle valves in the water line under suflicient pressure so that there can be no blow-back into the. water line; The water issuing from the needle valves may be passed into a coil immersed in ,the fused salt bath to convert the water int'o.v steam which will blow into the bath itself. in the controlled amounts desired The converter coil" will not be madeof any electrodepositable metal such as copper whether the operation is under electrolytic or under non-electrolytic conditions. In place of, injecting water or steam into thefused salt bath,,

hydrogen gas obtained from the cracking of ammonia. or natural gas, may be injected. A. convenient test as towhether' it may be desirable to-inject. any such substance ,may be obtained by dippinga piece of clean'metal into the bath to determine whether or not it wiilzbe stained withthe characteristic. tancolor of sodium oxide by such dipping.

Electrical conductor brackets 32 and 33 may be. mounted 'ininsulators 3'4supported on the respective sides of"vessel.1'.0', The. brackets 32v maybealterna-ted along. each side of and across: vessel 10 with.bracketsi33.= All the brackets 3.2 may beco'nnected. in parallel. by'a con duc'torf wire 36to a positive direct currentsource such,

as onefr'oma motor-generator set or an A. C. rectifier.- Anodic electrodes 37" are respectively suspended inside.- ves'selyl'Oi from eachbracket 32 so that the lower portions:

thereof: extend intothe-fused salt13 on oppositersidesof.

the work.2f6. as it passes. between the sinker rolls, 25';

Similarly, thebrackets 33 areconnected in parallelby'a,

conductor wire 38 to the negative pole. of. the directicurf rent source.

salt .13 adjacent to andon opposite sides of thework,.26;

be avoided In the operation of my new system under-electrolytic conditions utilizing equipment, one form of whichis illus trated-in Figures 1"t'o 3; cleaning, deoxidizing,descaling and/ordes'anding may quickly, conveniently and etficiently be performed. In generalg'the impressing ofa Cathodic electrodes. 39 are. suspended from. cachicondilctorbracket 3'3' and alsoextend into the. fused,

voltage across that portion of the bath of my new salt in fused condition surrounding the work between the sinker rolls 25 at the time being will generally enable my new system to be carriedout at a somewhat lower temperature or in somewhat less time or with a combination of both such advantages. Moreover, the electrolytic phase of my new system can be employed with advantage in the treatment of work the surface of which is extremely heavily rusted, scaled or. sanded. The action of my new composition in its fused state appears to be speeded up when electric current is flowing between the electrodes such as the respective electrodes 39 and 37 through that part at least of the work suspended or moving therebetween out of contact with anyof those electrodes. .For example, except in the case of simultaneous heat treating, my new bath system under electrolytic conditions will generally not be held at a temperature exceeding about 1150 F. Usually, a voltage across the respective electrodes 37 and 39 of from about 2 to about 30 volts and a current which may go as high as several hundred amperes from a minimum of about 20 amperes will suffice. While the operation illustrated in the figures has been described in connection with the use of direct current, it is also possible to operate satisfactorily while reversing the polarity of the current to obtain a corresponding reversal of current flow through the bath and the Work in the bath.

In the electrolytic phase of operations utilizing my new system, a temperature range between from about 700 F. to about 800 F. will usually be sufiicient to clean or to remove sand or oxides in the form of scale from the surface of ferrous and nonferrous work of metal. The time of such treatment may be variedfrom about seconds to about 2 hours, with satisfactory results in normal situations occurring in the course of a time of treatment extending between from about 15 seconds to about minutes. Further, the increased activity of my new system under electrolytic conditions will enable the most adherent material on the surface of ferrous and neuterrousmetals including titanium and its alloys to be substantially loosened and removed. Moreover, it appears that if the current is left in an electrolytic operation although there is at that time no work in the fused salt bath of my new composition, the introduction of the next lot of work may be processed relatively even more quickly in achieving the desired removal of scale, for example. Possibly, this even more heightened activity results from an increased rate of reduction of the scale because of the presence in the bath of a relatively larger amount of alkali metal which would seem to be composed almost entirely at least of the metal sodium.

In both non-electrolytic and electrolytic operations of my newsystem, there appears to be a reducing action or at least a suppression of any tendency of the fused salt in the bath to oxidize as well. as a suppression of contamination therein or the undue formation or suspension of sludgy or solid contaminants and reaction products. Such seems to be the case whether sand is being removed from castings, or graphite or carbon, grease, dirt,.enamel, paint or other material'is being cleaned oif metal surfaces, or whether descaling is being undertaken. Without being limited to my theory of operation, it appears that my new fused salt bath system may pick up some moisture from the air and that the alkali earth metal halide at least may also help to keep the bath in relatively clarified and stabilized condition. Such stabilization is indicated by the activity of the new fused salt remaining at satisfactory levels of operability.

In some cases, whether in an electrolytic or non-electrolytic operation, some water or steam may be admitted to the fused salt bath as through pipes when valves 31 are opened. The moisture so picked up or added never even approaches any quantity sufficient to render the fused salt bath an aqueous one in character. to help prevent any undue formation or build-up, possibly The moisture seems quality or quantity of the work produced.

in the case of the continuous treatment of strip as dis tinguished from the batch treatment of castings, forgings or other individual pieces of work. Whenever the level of the salt bath in the containing pot or vessel begins to be appreciatively lowered after continued use, additional salt in a dry state and conforming to my new composition being used may be added directly to the bath to raise the level to the desired point. Because of the resistance of my new salt bath system to. oxidation and contamination, treatment therein can be continued relatively speaking for longer periods and on greater tonnages than has heretofore been possible without adversely affecting the In the case of large tonnages or heavy pieces of work being treated at a single time, any tendency thereof to reduce the temperature of the fused salt bath as it is being immersed may be counteracted by preheating the work to the temperature of the salt bath.

The following illustrations of the manner in which my new salt bath system will work are not to be deemed limitations in or on the practice thereof. Thus, in using my new salt having an approximate composition, dry and by weight, of NaOH, KOH, 6%; and BaClz, 4%, under non-electrolytic conditions, will treat gray iron castings to clean, thoroughly desand and heat treat them when immersed in a fused bath of such salt for a period of about 5 minutes at a temperature of about 1225 F. Thereafter, the castings may be cooled in air for a short period, quenched in water, given a neutralizing rinse in dilute mineral acid such as sulfuric acid or hydrochloric acid, water rinsed, dried and given a soluble oil dip to prevent corrosion in storage.

Again, a fused bath having my new salt with an approximate composition on a dry weight basis ofNaOH, 88%; KOH, 6%; BaClz, 5%; and, with an addition ingredient in the form of, NaF, about 1%, will remove all trace of surface graphite from gray iron and alloy castings in less than 5 minutes when treated, under non-electrolytic conditions, between from about 850 F. to about 1150 F. Such treatment of the castings for about 4 minutes from about 1150 F. to about 1250 F. will further uniformly anneal such castings as well as clean them. Ordinary hot-rolled carbon steel treated off the hot mills at about 950 F. for about 2 minutes will be freed of oxides following which the steel may be water-quenched and dipped, for example, in dilute (e. g. 8%) sulfuric acid or muriatic acid for about 1 minute. Similarly, low chrome steels (4% to 6% Cr) treated for about 7 minutes at about 950 P. will be cleaned of heavy scale following which they generally will be water-quenched and dipped in dilute mineral acid at about F. for about 2 minutes leaving a White unetched surface. The foregoing illustrations are also under non-electrolytic conditions.

As illustrations of possible electrolytic applications of my new system, a salt mixture having an approximate composition, on a dry weight basis of, -NaOH, about 92%; KOH, about 2% and BaClz, about 6%, will, when reversing the respective direct current anodes like electrodes 37 cathodes like electrodes 39 atone-minute intervals, remove scale from stainless steel work in about 5 minutes utilizing a temperature in the range between from about 750 F. to about 1000" F. Such treatment for about 10 minutes reversing the polarity of the electrodes midway through the treatment period will not only remove such scale but also leave a glossy finish on the work being treated. A temperature in the neighborhood of 950 in theafused -salt bath ofil'my'new system under electrolytic conditions: will generally be an: optimum one; whenever heat treating: is: not simultaneously intended-tot bo' achieved.

Another electrolytic application: utilizing: my new' salt with: the-immediately foregoing approximate composition and with the admission of steam toithefused bath, will completely remove: scale from. stainlessiste'ellwork. in. about 6/minute's1ati a.- temperature between: from about 7 50 F. to about 1000"F., the polarity of the respective electrodes being: reversed at the 1 end. of: successive intervals such' as 1 minutepZminutes; 1 minute andi 2 minutes=of operation respectively. A- maximum ofi 10" minutes of such treatmentlwillz usually'suflice in even the'most-i difiicult citemova'li problems: The immediatelyforegoing treatment by my new system. may: be followed" by water quenching the work; ands then: dipping it into) dilute (e. g. 5%) sul-- furic acid' then into: dilute-nitric acidto which: some hydro-- fluoric acidmay' be addedt. The-after treatments of the wm-k after being subjected to my: new salt'bath system is a: matter: which. will: be well understood by-* those in the after-treatment art: My newtreatmentlleavesi-the workv in; such. condition that? no. unusual, protracted or unduly expensive: after-treatments: are-required to leave the sur face of; workimetallurgicallyneutral; cleanand dry.

It. will" be: clean that my new salt composition and treat-- ing system may be used in a variety of applications on a variety of typesof metal work without departing from the scope hereof. Thus, in the-reclaiming of -metals; my" system can. be employed for the removal of grease, dirt, enamel, or frit', or to' strip paint-on lacquerfrom metal partsandisurfaces. It may alsolreused for the removal of: rust retoo lead coatings, graphite, silicon, or car'- bon: compounds andv to prepare metal surfaces for sub-- sequent galvanizing, tinning or other" coating or treatment'. In the case of castings my invention can be usedto remove the sand therefrom and, if desired, at the same time to heat treat such casting; Inthe case of forgings, my new system can beused to remove scale therefrom and again, if desired, to anneal or otherwise heat treat the forgings. My invention will work substantially on all types of steelsand" alloys and in continuous strip-orbatch: operations. The new composition anditreatingsystem set-forth herein are not'to be' limited by the mere uses to which such may be applied, or by mere variations in= theproportions of the ingredients; or by changes in the operating conditions under whichithe' compositions are to-be used, or' the" type of work treated,

to 'the extent that such arc'within'the spirit'of this inven:

tion and the scope oftheappended claims.

1' claim:

1. In a salt bath system, a composition consisting essentiallyof, sodium hydroxide from about70'%1 to about 98%; potassium hydroxidev from about 0.5% to about. 12% and the balancesubstantiallyan alkaline earth metal halide;

2. In a salt-bathsystem, a composition consisting essentially'of, sodium hydroxide from about 70% to about 98% potassium hydroxidefrom about 0.5% to.about 12% and barium-chloride from about 0.5% to about. 20%.

3. lira salt bath system, a composition consisting essentially'of; sodium hydroxide. from about 85%. to about 95%, potassium hydroxide from about 0.5% to about. 4.5%" and barium chloride from about 0.5% to about. 12%., such saltto be used in a fused state. under nonelectrolytic conditions.

4". In asalt bath system, a composition consisting es- 12%,. and; barium: chloride from: about; 0.5%; to about. 20%;, such salt being adapted to: be: used in: a fused: state" under electrolytic conditions.

6.. In. a salt: bath system, a. composition consisting esw sentially' of, sodium. hydroxide, about. 98%; potassium:- hydroxid'e',,about1.5.%; an'dban'um chloride,- about 015% such salt: being adapted to. beusedin a. fusedstaterunder' electrolytic conditions.

7;. In. a. method: for metal treatment. by an. anhydrous salt bath. system, the steps comprising, immersingr work of metal having a surface to be-cleaned in. atfused com.- position consisting: essentially of sodium hydroxide as the preponderant' ingredient, potassium hydroxide and analkaline earth metal halide at. a temperature between about: 650" E1 and about: 1350- F. for a sufficient time to clean said surface.

8. In a method for metal treatment by'an anhydrous; salt bath system, the steps comprising, immersing work; of metal having a: surface to be cleaned of" grease, dirt and-lighter oxides in a fused composition consisting-es sentially of' from about 70% to about 98% of sodiunrhy=- droxide: as the preponderant ingredient, from 0.5% to 12% ofpotassium hydroxide and the balance'substantiallyan alkaline. earth metal halide at a. temperature from about: 800. F. to about 900 F. for a sufficient time to complete the cleaning of said surface.

9. In a method for metal treatment by an anhydroussalt bath system, the steps'comprising, immersing work of metal having a surface to be' descaled in a fused com-= position.consistingessentiallyof'from about 70% to about 98% of sodium hydroxide as' the: preponderant ingredient, from. 0.5% to 12% of potassium: hydroxide and the:balancesubstantially an alkaline earth metal chloride at atemperature from: about 900 F. to'- about" 1050"" F'. for a sutficient time to descale said surface.

10. In-a method for' metal treatment by an anhydrous salt bath. system, the steps comprising, immersing work of. metal. having. a surface to bedeoxidize'd in a fused composition consisting essentially of from about 7096- to about 98%: of sodium hydroxide as the preponderant ingredient', from 0.5% to 12% of potassium hydroxideand" the balance substantially an alkaline earth-metal chloride atiatemperature from about 650 F. to about 135.0"' F; for a. period of timefrom about 15 seconds to about 2 /2 hours until said surface is deoxidizedL ll. In a methodfor metal treatment by an anhydrous:- salt bath system, the steps comprising, immersing" work" offmetal. to be heat treated and having a surface to' be deo'xidize'd'in a fused composition consisting essentially of from about 70%to about'98% of sodium hydroxideas the preponderantingredient, from 0.5% to 12 of potas sium hydroxide and the balance substantially an alkaline earth. metal halideat a temperature-from about 000" F. to about. 1300"" F. fora" sufficient time to deoxidizesaid surface and heat treat. said. work:

12. In a method form'etal treatment by an anhydrous salt bathsystennthe steps comprising immersing castings andthelike-of metal having'a surface to be d'esand'ed-iit a fused composition consisting essentially of from about- 70 to about 98% ofsodium. hydroxide as the pre* ponderant' ingredient, from about'0l5% to 12% of potas sium' hydroxide and. the balance substantially an alkaline earth metal halide at a. temperature from about 900"PE to about 1350"" F. for a sufiicient time todesand said surface.-

13. In a method for metal treatment by ananliydrous' salt bath system, the steps= comprising immersingwork of metal having a surface to be cleaned in a fused salt bath" consisting essentially of from about 70%= to about 98% of sodium hydroxide as the'prepond'erant ingredient; from' about 0.5% to 12% of potassiumhydroxide; 015% to 550% sodium fluoride,- and barium chloride as the bal ance, at a' temperature'fi'om' about 650 to about 1350*Fi' for asufiicient time to'clean' said surface;

l4; In ametiiod'for'metal treattncntiby an anhydrous 9 salt bath system, the steps comprising, immersing work of metal having a surface to be cleaned in a fused composition consisting essentially of from about 70% to about 98% of sodium hydroxide as the preponderant ingredient, from about 0.5% to 12% of potassium hydroxide and 5 the balance substantially an alkaline earth metal chloride at a temperature frorn about 650 F. to about 1350 F., introducing steam into said fused salt bath during said immersion and continuing said immersion for a time 10 sufiicient to clean said surface.

' References Cited in the file of this patent UNITED STATES PATENTS Kelvie Apr. 14, I936 Tainton Oct. 25, 1938 Young July 10, 1945 Spence et a1 Feb. 26, 1946 Webster Jan. 11, 1949 Webster Apr. 19, 1949 Holden Aug. 2, 1949 Brisse Nov. 14, 1950 Dunlevy Apr. 14, 1953 

1. IN A SALT BATH SYSTEM, A COMPOSITION CONSISTING ESSENTIALLY OF, SODIUM HYDROXIDE FROM ABOUT 70% TO ABOUT 98%, POTASSIUM HYDROXIDE FROM ABOUT 0.5% TO ABOUT 12% AND THE BALANCE SUBSTANTIALLY AN ALKALINE EARTH METAL HALIDE.
 7. IN A METHOD FOR METAL TREATMENT BY AN ANHYDROUS SALT BATH SYSTEM, THE STEPS COMPRISING, IMMERSING WORK OF METAL HAVING A SURFACE TO BE CLEANED IN A FUSED COMPOSITION CONSISTING ESSENTIALLY OF SODIUM HYDROXIDE AS THE PREPONDERANT INGREDIENT, POTASSIUM HYDROXIDE AND AN ALKALINE EARTH METAL HALIDE AT A TEMPERATURE BETWEEN ABOUT 650* F. AND ABOUT 1350* F. FOR A SUFFICIENT TIME TO CLEAN SAID SURFACE. 